The surface area of a cube is decreasing at the rate of 15 sq. cm/sec. Find the rate length of the edge is 5 cm.

Explanation

Let s be the surface area of a cube. Let x be the length of each side of the cube.
`then s = 6x^2 rArr ds/dt = 12x dx/dt`
Given that `ds/dt = 15 sq. cm/sec. and x = 5 cm`.
Then - 15 = 12 xx 5 dx/dt`
`rArr dx/dt = - 15/60 = - 1/4 = -0 cdot 25 cm/sec`.
therefore The edge is decreasing at the rate of 0 cdot 25 cm/sec`.